Solar energy power system

ABSTRACT

A solar energy vapor (freon) powered system for generating electrical energy in which a portion of the heat absorbed from the sun in daylight is stored for use during darkness by a thermal capacitor in which a mass of Pyrone, having a high thermal capacity, liquifies when heat is applied to it and goes through a solidification process to provide a heat output. A highly efficient solar boiler is constructed utilizing an anodized titanium surface and a particular combination of shaped boiler tubes and complementary reflectors. The overall efficiency of the system is further improved by a unique arrangement of heat recovery devices.

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the UnitedStates Government and may be manufactured and used by or for theGovernment of the United States of America for Governmental purposeswithout the payment of any royalties thereon or therefor.

This is a division of application Ser. No. 421,702, filed Dec. 4, 1973,now U.S. Pat. No. 3,903,699.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to solar power systems and particularly to asystem of this catagory adapted for employment in outer space.

2. General Description of the Prior Art

The idea of generating electrical power from heat from solar energy isof course not new. The problem is that of achieving an efficiency tomake such a system feasible. The problem has two particular aspects. Oneis that of efficiently translating solar energy into a heated workingmedium; and another is achieving sufficient efficiency in theutilization of the working medium. It is believed clear that before awide spread use of solar energy can be expected that significantimprovements must be made in both these areas.

It is, accordingly, one object of this invention to provide a solarboiler capable of greater effectiveness in converting solar radiationinto a heated work medium and another to provide an overall system forthe generation of power from it with improved efficiency.

SUMMARY OF THE INVENTION

In accordance with the invention, a solar energy type power generatingsystem is constucted wherein a low boiling temperature fluid, such asfreon (T.M.) 114, is vaporized in a solar boiler and employed to operatea turbine. To maintain operation of the turbine in the absence ofsunlight, the system includes a thermal storage device which contains ameltable substance such as pyrone (trade name), C₇ H₈ O₂, which ismelted to a hot liquid by a portion of the solar boiler heat duringdaylight and thus accumulates heat. Then during periods of no sunlight,vapor is generated by the thus stored heat to operate the turbine. Asone further feature of the invention, the solar boiler employs ananodized outer surface, particularly a blue anodized surface. This, ithas been found, enhances the effectiveness of translation of the sun'srays into useful heat. Further, this surface, when polished, provides animproved ratio of heat absorption to heat emission and thus an improvedoverall efficiency for the system. The system further includes means forrecovery of what would otherwise be lost heat and still further includesa combination solar boiler and radiant condenser assembly whichparticularly facilitates employment of the system with spacecrafts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictoral view of an embodiment of the invention as it wouldbe used in conjunction with a spacecraft.

FIG. 2 is a schematic illustration of the system of this invention.

FIGS. 3 and 3a are perspective views of a portion of the solar boiler ofthe invention as shown in FIG. 1.

FIG. 4 is an enlarged perspective view of a portion of a solar boiler ascontemplated by this invention.

FIG. 5 is a perspective view of a portion of one of the boiler tubeassemblies shown in FIG. 4.

FIG. 6 is a perspective view of a gas separator employed in the systemshown in FIG. 2.

FIG. 7 is a diagrammatic illustration of a thermal capacitor employed inthe system shown in FIG. 2.

FIG. 8 is a perspective view of a portion of a radiant condenseremployed in the system shown in FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a spacecraft 10 equipped with a power system 12 suppliedvapor pressure by boiler 14 (FIG. 2). Electrical generating equipmentand certain other portions of the system are contained in cylindricalhousing 15 having a conical end 16 connected by boom 18 to spacecraft10, boom 18 supporting the power system and providing internalpassageway for fluid lines and electrical cables connecting to thespacecraft. FIG. 1 particularly illustrates two T-shaped, collapsiblesolar boiler-radiant condenser arrays 20 and 22 which heat a workingfluid for a turbine-operated generator and condense the fluid outputfrom the turbine, respectively. Each array employs a solar boiler orheat collecting panels 24 and radiant condenser or radiating panels 26.Heat collecting panels 24 generally conform to vertical planes (asshown) with forward sides of the panels (opposite to facing side shownin FIG. 1) being adapted to be illuminated by and to intercept maximumradiation from the sun.

Conversely, heat radiating panels 26 extend substantially planar from acentral region of the collector panels at an angle normal to andrearward of the collector panels and thus they are always shaded by thecollector panels from the sun.

Further, in use, each radiating panel 26 is always pointed edge-on tothe earth for minimum albedo effect and maximum view of deep space whilestill remaining in the shadow of the collector panels 24, individuallydesignated 30 and 32.

Referring now to FIG. 2, there is shown a block diagram of a closed looppower system 10 constructed in accordance with this invention. Itemploys a low temperature boiling fluid, such as freon 114, to operate aturbine 36 which in turn drives an alternator 38. As one means ofreturning heat to the system, and the system employs several such means,heat exchanger coil 40 is heat coupled to alternator 38. The fluidoutput of turbine 36, a superheated working fluid, is fed throughregenerative heat exchanger 42 to radiate condenser 26.

Pump 46 is connected to the output of radiant condenser 26 and it pumpscondensed or liquid freon to spacecraft heat exchanger 48 along twopaths. One path is back through pipes 50 and 52 to heat exchanger coil54 which functions to pick up heat from coil 56 and preheat the liquidfreon before it is fed to boiler 14. The other path is directly tospacecraft heat exchanger 48. Flow is through a flow dividing valve 60which is adjustable to vary the ratio of flow of fluid between thepaths. In this fashion, a desired degree of heat may be transferredaround radiating condenser 26. Spacecraft heat exchanger 48 includesliquid lines coupled to spacecraft 10 to absorb heat given off byequipment in the spacecraft. Thus, spacecraft heat exchanger 48 providesa second stage of liquid preheating. The liquid output of spacecraftheat exchanger 48 is pumped by pump 78 through heat exchanger coil 40,coupled to alternator 38 and thence to valve 62. Coil 40 absorbs heatlosses from alternator 38, and in so doing, functions as a third stageof liquid preheating. At this point, equipment coupling is in either oneof two modes. In one, a daylight operating mode wherein the sun isactively heating solar boiler 14, valve 62 will be as shown and fluid inline 64 will pass downward through valve 62, through line 66 to boiler14. The fluid is then heated in boiler 14 and the resulting workingfluid flows through check valve 68, flow divider 70, gas separator 72,to the inlet of turbine 36 to power it.

Flow divider 70 enables a portion of the freon vapor to be applied tothermal capacitor 74 which functions, as described below, to absorb andstore heat. This transfer of heat causes the vapor to be condensed andthe resulting liquid freon passes through siphon 76 and down throughvalve 62 and is forced back to solar boiler 14. Siphon 76, which is alsoconnected to gas separator 72, functions to siphon liquid collected ingas separator 72 and forces it back through valve 62 to boiler 14. Pump78 provides a pressure which enables the return flow to boiler 14.

During periods when solar boiler 14 is in the dark and thus receiving noheat from the sun, valve 62 is operated to the dashed line position, inwhich case the fluid flow is from line 80 and in the reverse directionthrough siphon 76 to thermal capacitor 74 where it picks up heat and isboiled by the previously stored heat in thermal capacitor 74. Checkvalve 68 prevents flow from line 82 back through solar boiler 14 andthus working fluid flows up through line 84, then down through gasseparator 72 to turbine 36. Siphon 76, again due to flow through it,draws residual liquid accumulated in gas separator 72 and cause it to bereheated in thermal capacitor 74.

A particular feature of the system is solar boiler 14 consisting of twosimilar panels 30 and 32 which are, as previously mentioned, disposed onopposite sides of cylindrical housing 15 (FIG. 1). Since these panelsare similar, only one panel, panel 30, will be described in detail. FIG.3 shows an enlarged version of a portion 31 of panel 30 as viewed fromthe rear side, or the side away from the sun (FIG. 1). Each of panels 30and 32 includes a plurality of spaced collector assemblies 86 into whichsolar energy is directed by pivotally interconnected reflecting panels88. A pair of panels 88 form a V-shaped channel to direct the sun's raysonto each opposing surface 90 of laterally disposed tubes 92 of each ofsolar collector or boiler assemblies 86 (FIG. 4). Each of boilerassemblies 86 includes a predetermined number of tubular elements ortubes 92 commensurate with a desired output power.

Tubes 92 are typically formed from a length of heat conductive materialsuch as aluminum, etc., and are diamond-shaped in cross section (FIG.5). Each tube 92 includes six longitudinal, essentially triangular,recesses or passages 94 and two cylindrical passages 96 through whichthe working fluid is circulated. The outer faces 98 are then coated witha thin layer of copper 100 or other suitable material which is adaptedto receive as a bonded surface an outer skin member 102 such as titaniumalloy Ti 6Al 4VA.

Exposed surface 90 of the titanium is then anodized so as to produce adesired shade of blue. This shade occurs when the absorptivity (α)ranges from 0.70 to 0.74. The surface is polished until the emissivity(ε) is between 0.15 and 0.16.

When the tubes 92 are supported as described below, the effectivesurface characteristics are improved such that effectively α = a maximumof 0.97 and ε = a maximum of 0.24. Accordingly, a very efficient anddependable solar boiler can be constructed at much less expense than byutilizing other known techniques of surface treatment and mounting ofcollector elements. Referring to FIG. 4, tubes 92 are supported by endplates 104 and 106 and the apices 108 of obtuse angles of each ofdiamond-shaped tubes 92 are joined in mating alignment as shown in FIG.4. When thus mounted, exposed surfaces 90 are displaced at an angle of60° with respect to each other such that any ray 110 of the sun,reflected from any reflector 88, impinges on one surface 90 fromreflector 88 and then to the adjoining surface 90 wherefrom it isdirected along the same path back to the original surface 90 and to thereflector 88. Thus, there is achieved a three-point contact withsurfaces 90 of tubes 92. Once the tubes are assembled to end plates 104and 106, end covers 112 and 114 are sealably joined to support plates104 and 106, respectively, through which working fluid is circulated byway of Y-shaped fittings 116, only one being shown, FIG. 4. Whencombined as shown in FIG. 3, collector assemblies 86 are interconnectedby lengths of flexible hose 118 which enable each of arrays 30 and 32 tobe folded in accordian fashion during a launch phase of a spacecraft.

During sunlight periods, as previously described, working fluid ispumped by pump 78 (FIG. 2) through heat exchanger 40 of alternatorassembly 38, thence through diverter valve 62 into solar boiler 14.Working fluid is supplied to each of arrays 30 and 32 (FIG. 3a) byexternal feeder pipes 120 (only one being shown), which interconnect tothe input end of flexible hoses 118. Hoses 118 are adapted to act as aninput manifold, being of decreasing diameter toward the outer end 122 inorder to distribute the working fluid through collector assemblies 86 atan essentially equal rate of flow. Fluid is forced under pressurethrough solar collectors 86 and thus extracts heat from interconnectingof boiler tubes 92 whereupon it is passed through inerconnecting hoses124 (FIG. 4) at the opposite end of assemblies 86, which are connectedto return feeder pipe 126 (FIG. 3a). Thence, flow is to input line 82 offlow divider valve 70 (FIG. 2). Heat energy from solar boiler 14 in theform of heated vapor is thus selectively divided by flow divider valve70, and the portion not needed to drive turbine 36 is stored in thermalcapacitor 74 for use during the next period of darkness.

Output line 84 couples flow from flow divider valve 70 to input 128 ofcentrifugal gas separator 72 (FIG. 2). Gas separator 72 (FIG. 6)includes an essentially doughnut-shaped enclosure 130 into which gasesare tangentially injected under pressure from flow divider valve 70.This high velocity gas spins the gaseous liquid contents of gasseparator 72 causing liquid and heavier particles to be forced outwardfrom central opening 132. The liquid content is then extracted at output134, formed in outer wall 136 and coupled to the input of siphon 76. Drysaturated gas is discharged around baffle 138 through central opening140 of gas separator 72 and is then fed to the input of gas turbine 36.

As mentioned above, that portion of vaporized gases not needed forimmediate use to drive turbine 36 is fed by way of flow divider valve 70through line 82 into the input of thermal capacitor 74 (FIG. 2). Thermalcapacitor 74 (FIG. 7) includes rectilinear container 142 which ispartially filled with a solid wax-like material, such as that known bythe trade name Pyrone, having the chemical designation C₇ H₈ O₂. Thismaterial absorbs approximately 100 BTU's per pound as it melts at 270°F.and releases the same amount upon solidification. Vaporized gases fromsolar boiler 14 are fed through thermal capacitor 74 by means of afin-tube assembly 144 which is immersed in the wax-like material. Onceheat is extracted from the vaporized gas within thermal capacitor 74, itflows through siphon 76 and thence back to the input of solar collector14. Residual liquid from gas separator 72 is picked up by siphon 76 andis fed in parallel through valve 62 with liquid from boiler feed pump 78(FIG. 2) to the input of solar boiler 14. The liquid is then reheated toa vapor in the cycle described above wherein gases from the output ofsolar boiler 14 are again fed to the input of flow divider 70. The abovecycle of operation continues as long as the spacecraft is in sunlight.Electrical power is available from alternator 38 on power lines 147 toprovide electrical power to spacecraft 10.

A cycle of operation while in earth's shadow is as follows. Uponentering this phase of orbit, diverter valve 62 is switched to theposition shown by dotted lines 146 (FIG. 2). Boiler feed pump 78 nowpumps liquid freon through valve 62 into what was formerly the output ofthermal capacitor 74. Check valve 68, located in the output line fromsolar collector 14, is now closed by back pressure through thermalcapacitor 74. As liquid freon is pumped backward through thermalcapacitor 74, input line 82 now becomes the output of thermal capacitor74 and gas flow is still through output line 84 of flow divider valve 70downward into gas separator 72. As a result, liquid freon is heated bythe molten material within thermal capacitor 74 and this materialsolidifies as it gives up heat. Dry saturated gas from the output of gasseparator 72 is coupled into turbine 36. Residual liquid is fed fromoutput 134 of gas separator into the input of siphon 76. Liquid fromvalve 62 which is flowing through siphon 76 into thermal capacitor 74picks up residual liquid from gas separator 72 and pumps it back intothermal capacitor 74 where it is again vaporized and thence fed intoflow divider 70. Thus, during operation while the spacecraft is withinthe earth's shadow, working fluid is vaporized by heat stored in thermalcapacitor 74 from a previous cycle of operation in daylight hours.

Superheated gas from turbine 36 is coupled through one coil 56 of heatexchanger or regenerator 42, as described above, and through feeder line148 (FIG. 3a) into one of a plurality of laterally disposed feedertunnels 150 of heat pipe radiator condenser assembly 44 (FIG. 8). Thesecondensing tunnels are interconnected by lengths of flexible hose 152 ina similar fashion to that described above with respect to solar boilerassembly 14. Thus, radiant condenser 26 may be folded in accordianfashion as described above during the launch phase of a spacecraftmission. The outlet or return end 154 of condensing tunnels 150 areinterconnected by flexible hoses 152 as are the input ends 156. Cooledliquid is returned through inlet feeder pipe 158 (FIG. 3a) to pump 46located within central housing 15. Each of feeder tunnels 150 is adaptedto mount a number of flexible heat pipes 160 which are supported onopposite sides of tunnels 150. A heat pipe is a known type of heattransfer device and is characterized by a sealed, elongated casing orpipe containing a heat transfer fluid and typically having a heat inputat one end and also having a wick adjacent to the inner periphery of thepipe which extends the length of the pipe. This configuration produces afluid circulation end-to-end of the pipe without the necessity of a pumpand thus provides an extremely efficient and effective heat radiatoralong the outer surface of the pipe. For further discussion of heatpipes and their operation, reference is made to U.S. Pat. 3,532,159. Inthe present case, a finned end 162 of heat coupling element 164 issupported within the interior of each condensing tunnel 150 and itproduces a heat transfer to the heat pipe. This heat is then circulatedaong the heat pipe and thereby radiated into space from the walls of theheat pipe.

Cooled liquid from pump 46 is selectively fed by valve 60 into a secondcoil 54 of heat exchanger 42 (FIG. 2). Thus heat from turbine 36 isrecovered by regenerative heat exchanger 42 and fed to a second input ofvalve 60, the output of which is then connected to spacecraft heatexchanger 48, wherefrom it is again recycled through boiler 14 (FIG. 2),as previously described.

From the foregoing, it will be apparent that the applicant has providedan improved system for extracting heat energy from the sun. While thisinvention is particularly directed to applications for providingelectrical power for spacecrafts, the principles and means disclosedherein are applicable, in many cases, to earth installation.

What is claimed is:
 1. A solar boiler comprising:a reflector assemblycomprising at least one V-shaped channel; and a plurality of elongated,diamond-shaped fluid coupled tubes lying generally within said V-shapedchannel and along a plane which bisects the apex of said V-shapedchannel and which plane intersects opposite edge pairs of corners ofeach tube, the tubes extending lengthwise in a direction parallel withsaid channel; whereby solar radiant energy striking said reflector isdirected onto the surface of one tube and then over to the surface of anadjacent tube.
 2. A solar boiler as set forth in claim 1 wherein saidouter surface of said boiler tubes is of anodized titanium and saidsurface is blue.
 3. A solar energy power system as set forth in claim 2wherein said outer surface has an absorptivity of from 0.70 to 0.74 andsaid surface has an emissivity of between 0.15 and 0.16.